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Re: Chicxulub's Antipode (Re: cause of death at KT)
Phillip Bigelow wrote:
As an aside:
I read a paper some years ago about how tsunamis would interact with
different geometries of land masses. The paper was mostly theoretical,
but very revealing. It turns out that if a tsunami in deep water hits a
hypothetical vertical wall of land (i.e., a wall extending from
bathyal/abyssal depth to the surface), the surface expression of this
collision will be a plume of water traveling a thousand+ feet *straight
upward*. Not the usual slosh-over-land scenario seen on typical
coastlines. Vertical walls also reflect a substantial percentage of the
tsunami (think of a standing wave). In nature, no such geometry exists
on that scale, the closest being undersea volcanos with 70-80 degree
slopes (but they don't form walls of rock).
There are huge near vertical cliffs off the coast of western Tasmania -
I remember seeing the images a few years ago when they were first
mapped, and they are spectacular. I found a reference to them at
http://www.agu.org/sci_soc/exon.html#figure1, but unfortunately the
images won't load into my browser. The text is still of interest, though:
"The South Tasman Rise, a submerged continental block larger than
Tasmania, extends from 44° to 50°S. About three-quarters of it, or
150,000 km², was mapped (Figure 1
<http://www.agu.org/sci_soc/exon.html#figure1>). The rise only sank
completely below the ocean in the last 40 m.y., and parts of it are less
than 1000 m deep. Spectacular faults and giant fault blocks were seen in
water depths of 2500-4500 m on its western and eastern sides. The
submarine cliffs dwarf anything on Australia, reaching 2300 m high in
one place, and have slopes averaging 20° (Figure 3
<http://www.agu.org/sci_soc/exon.html#figure3>). The rise is
current-swept, so Neogene sediment cover is thin or absent. It consists
of about 20% outcropping rock and 80% sedimentary cover and has outcrops
of ancient basement rocks like schist, gneiss, granite, and Paleozoic
sediments, as well as younger Mesozoic sediments and Tertiary basalts."
Cheers
Colin
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Colin McHenry
School of Environmental and Life Sciences (Geology)
University of Newcastle
Callaghan NSW 2308
Australia
Tel: +61 2 4921 5404
Fax: + 61 2 4921 6925
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